1. Field of the Invention
The present invention relates to an optical fiber catheter, and more particularly to as arrangement of optical fibers within an optical fiber catheter, near its distal end.
2. Description of Related Art
Many teachings exist in the art for using optical energy delivered through a fiberoptic catheter assembly to ablate obstructions within blood vessels. One such teaching is revealed in the U.S. Pat. No. 4,844,062, to Wells. Wells uses a laser catheter to ablate an area larger than the cross-sectional area of a single fiber or fiber bundle inside the catheter. This is done by rotating the fiber or fiber bundle, which covers the center of the catheter, around a guide wire that is eccentric inside the catheter. Since only a single fiber or bundle is employed, only a small area, albeit larger than the cross-sectional area of the fiber or bundle, can be ablated.
Kitrell et al., in his U.S. Pat. No. 4,913,142 discloses a laser cathether containing optical fibers for carrying laser light. A shield is mounted on its distal end for displacing intravascular blood and preventing the fiber from the blood's corrosive contents.
Other examples include U.S. Pat. Nos. 4,207,874, to Choy, 4,587,972 to Morantte, Jr. 4,622,972 to Giebeler, Jr., 4,790,310 to Ginsburg et al. 4,832,023 to Murphy-Chutorian et al. and so on.
However, none of the above-mentioned patents address the issue of providing a highly flexible optical fiber catheter for ablating a large target area without requiring an extremely powerful laser. When the desired ablation area is large, conventional thinking requires that an optical fiber catheter with a correspondingly large distal diameter be used. For such a catheter to ablate the area uniformly, a large number of optical fibers must be packed within the outer lumen of the catheter (See FIG. 1). For example, constructing a catheter of 2 mm in diameter or larger requires 80 or more 100 micron fibers. Furthermore, the cross-sectional area of a laser catheter, which varies directly with the required number of optical fibers to fill it, increases in proportion to the square of its diameter. The number of required optical fibers for packing the catheter can become prohibitively great as the required diameter increases. Increasing the number of fibers decreases the flexibility of the catheter.
In addition, as the number of optical fibers becomes large, more power must be delivered by the energy source that drives the fibers. In the above example with 2 mm catheter, a laser must deliver more than 100 mJ.
Clearly, construction and operation of catheters for ablating a large target can become difficult and expensive.